Herpes Simplex Virus (HSV) ocular infections present a recurrent problem for hundreds of thousands of individuals in the developed world, with over 400,000 people affected by HSV infection of the eye in the United States alone. The ability of HSV to cause ocular disease is based on its extremely rapid transport and cell-to-cell spread within epithelial tissues, into sensory neurons and across neuronal synapses. These processes appear to be mediated by specialized viral mechanisms which sort virus particles to sites of cell- to-cell contact, promote transport of viral particles in a directed fashion within neuronal axons and lead to rapid spread between cells. The HSV membrane glycoproteins gE/gl mediate viral transport and spread in both epithelial tissues and neuronal tissues, while another membrane protein, US9, functions specifically in neurons and not in epithelial cells, to sort virus particles. This proposal seeks to determine how gE/gl and US9 function to promote HSV transport in neurons and spread of virus from neurons to epithelial cells and between neurons. Aim I will characterize the role of gE/gl and US9 in axonal movement of viral components in an in vitro neuronal culture system. Aim II will investigate the role of gE/gl and US9 in HSV spread from neurons to epithelial cells by using a compartmented chamber system. This system, while it recapitulates the cell-to-cell transmission of HSV observed in ocular animal models, is more streamlined to allow for the elucidation of the mechanistic details of spread. Aim III will investigate the role of gE/gl and US9 in HSV neuron-to-neuron spread in an animal model of ocular HSV infection. Overall, these studies will contribute to a better understanding of the fundamental pathways by which HSV is able to cause ocular disease. PUBLIC HEALTH RELEVANCE: HSV eye infections present a significant and continuing problem for thousands of Americans, with the potential to cause irreversible damage and blindness. Although treatments in the form of antivirals, steroid therapy and corneal transplants are available, they are not always successful and the incidence of recurrent infection is high. Thus, a better understanding of the basic mechanisms which this virus uses to cause ocular disease is required which will allow the design of better methods to deal with this ever present problem.